to an additional pattern (a subset) specified on the command line. For instance, a playbook could be reusable
and target "webservers" and "dbservers", but you want to test only in the stage environment, or a few boxes at a time.
./group_vars/groupname.yml (for all groups the host is in)
./host_vars/hostname.yml (for the hostname given in the inventory)
This requires an actual inventory file, not script and the paths are relative
to the directory of the inventory file.
get_hosts() was treating [] (meaning complete restriction, no hosts allowed)
the same as None (meaning no restriction, all hosts allowed). Fixed logic.